THIS INVENTION relates to a proximity transponder system.
A proximity transponder system comprises generally two operating units, namely a proximity reader and a proximity passive transponder, where the proximity passive transponder can be interrogated by the proximity reader. This interrogation can be associated with both read-only and read/write technologies.
Such a proximity transponder system utilizes inductively coupled coils associated respectively with the reader and the transponder, firstly to provide an energy transfer from the reader coil to the transponder coil and secondly to provide a mechanism for data transmission between the reader and the transponder. By providing for an energy transfer from the reader coil to the transponder coil, the need for a separate power source for the transponder is effectively eliminated. The inductively coupled coils generally are energised by means of an AC signal with nominal signal frequencies of 125 kHz and 13.56 MHz. Insofar as the operation of a proximity transponder system of the above type, and particularly of the operating units thereof, is already well known, this is not described in further detail herein. Various applications of proximity transponder systems, including applications relating to access control systems, also are well known and are not described in further detail herein.
It is known in relation to a proximity transponder system that the inductive coupling between the coils of the reader and the transponder is sensitive to any metallic object, e.g. a metallic plate, or the like, positioned within the gap separating the two coils. The effect of a metallic object is that it causes xe2x80x9cshortingxe2x80x9d of flux lines, such xe2x80x9cshortingxe2x80x9d resulting either in inductive coupling being interfered with, or being completely prevented. For this reason, each operating unit associated with a proximity transponder system has traditionally been constrained to the use of a nonmetallic housing for the electronic components of the unit, a housing for the operating unit of a proximity transponder system thus typically being formed of a synthetic plastics material. This restriction clearly is associated with disadvantages insofar as housings of a synthetic plastics material can be relatively easily tampered with and damaged and it is thus an object of this invention to at least ameliorate this problem, particularly by permitting either one or both of a reader and a transponder as herein envisaged to be located within a metallic housing that offers the advantages of robustness and strong resistance against vandalism.
According to the invention there is provided an operating unit of a proximity transponder system, which has a housing having walls formed at least predominantly of a metallic material and in which the walls, in the location of the induction coil of the unit housed in the housing, define a space that is configured to permit magnetic flux lines to pass through the walls of the housing via the said space and thereby to permit inductive coupling with the induction coil of another operating unit.
The space defined by the walls of the housing may be an open space defined by an aperture in the said walls or, alternatively, may be a closed space defined by a wall segment of a non-metallic material of a type that will not cause xe2x80x9cshortingxe2x80x9d of flux lines. For the latter configuration space, the said wall segment of a non-metallic material may be formed of a synthetic plastics material.
According to one particular embodiment of the invention, the housing of the operating unit has a front wall, a spaced rear wall and a surrounding side wall extending between the front wall and the rear wall, the induction coil of the unit is located adjacent one of the walls in a substantially parallel relationship therewith and the space defines a first segment, defining a perimeter profile that coincides substantially with the perimeter of the coil, and a second segment, that extends in a slot-like fashion radially away from the first segment for a sufficient distance to avoid xe2x80x9cshortingxe2x80x9d of the flux lines required for inductive coupling with the induction coil of another operating unit, in use of the unit. For an induction coil located adjacent the front wall of the housing, the first segment of the space is defined within the said front wall while the second segment of the space extends to a side edge of the front wall and along the side wall towards the rear wall of the housing.
The operating unit of the invention particularly may comprise either one of a proximity reader and a proximity passive transponder, of a proximity transponder system.
The invention extends also to a housing for an operating unit of a proximity transponder system in accordance with the present invention.
The overall configuration of such a housing clearly is greatly variable and in this regard it is envisaged that different configuration housings can be associated with proximity readers and with proximity passive transponders. Such housings for proximity readers and for proximity passive transponders will be configured to permit, in combination, inductive coupling of coils carried in such housings and, as such, effective communication between proximity readers and proximity passive transponders.